1. Field of the Invention
The present invention relates to rotatable magnetic information storage disks and more particularly to position indicating markings on such disks.
2. Description of the Prior Art
U.S. Pat. No. 4,157,577 of Porter et al for a "Rotatable Storage Apparatus with Digitally Responsive Circuitry for Track Selection" describes a magnetic recording disks with a magnetic spiral servo track and annular data tracks. The position information is encoded digitally in a series of track recorded on either side of each data track. This requires extra space on the disk to store the digital position indicating tracks.
U.S. Pat. No. 3,879,753 shows a phase-locked loop for use with a magnetic recording medium which synchronizes the clock of the phase-locked loop to the data signals detected from the magnetic medium. We found no suggestion there of a spiral servo track or a separate servo truck on the medium.
U.S. Pat. No. 3,898,690 of Desai for "Phase-Locked Loop for an Electronic Sectoring Scheme foro Rotating Magnetic Memory" assigned to Pertec Corporation describes use of a phase-locked loop to coordinate the detector with the sector servo on a disk.